Thunderstorms Flashcards
What cloud formation are thunderstorms associated with?
Cb
What is the definition of a thunderstorm?
One or more sudden electrical discharges in the form of a flash of light (lightning) and a rumbling sound (thunder)
3 requirements for a thunderstorm to form
- Deeply unstable air
- A lot of moisture
- A trigger to cause the air to rise
What is the key feature of the initial stage?
The cell only contains updraughts (30m/s/60kt
Lasts 15-20 minutes
What are the key features of the mature stage?
Updraughts (50m/s/10,000ft/min) and downdraughts (2,000ft/min or 6,000ft/min in a microburst) coexist
Rain begins to fall
Lasts between 15-30 minutes
What can a Cb do when the updraughts are strong enough?
Overshoot the anvil and punch through the tropopause
What happens in the dissipating stage?
The downdraught cuts off the updraught
The storm no longer has a supply of warm moist air
Light rain and weak outflow winds may remain for awhile, before leaving behind just a remnant anvil top
May last 1.5 to 2 hours
4 thunderstorm triggers
- Convection
- Frontal
- Orographic
- Low level convergence
4 thunderstorm types
- Single cell
- Thunderstorm cluster (multi cell)
- Squall line
- Supercell
Characteristics of a single cell
Form on warm and humid days
May be severe with hail and microburst winds
Multi cell thunderstorm characteristics
Multiple cells covering a large area
Individual cells can move in different directions to the cluster
Supercell characteristics
A single long-lived thunderstorm
Responsible for tornadoes and large hailstones
Squall line characteristics
A line of thunderstorms
What is a mesoscale convective system (MCS)?
Collection of thunderstorms that act as a system. Can spread across an entire state and last more than 12 hours. May appear on radar as a solid line, broken line or cluster
What is a mesoscale convective complex (MCC)?
Is a type of MCS. Large, circular, long lived cluster of showers and thunderstorms. Area of cloud top at least 100,000km^2 at a temperature of -32 degrees or a cloud top of 50,000km^2 at a temperature of -52 degrees
What is a gust front?
Downdraught air flows underneath the warm air inflow. Can spread up to 20-30km/15-20nm in front of the cell.
What are roll and shelf clouds?
Roll shaped clouds associated with gust fronts
What is a microburst?
Rapidly descending air that lasts up to 5 min with a diameter less than 4km, can occur multiple times in a single cell. Can be 50kt or 6,000ft/min
What is a macroburst?
Descending air that lasts between 5-20 mins normally greater than 4km in diameter, can occur more than once in a single cell
Biggest danger of downbursts
At low level during take-off and approach
What are the dangers of Virga?
Can generate intense downdraughts that can be difficult to detect
What is the danger of hail?
Can cause damage to the airframe, in particular the nose which is made from a weaker material in order to reduce radar interference
Where’s the best place to fly if approaching a cell?
On the windward side
Where’s the greatest risk of hail?
In the anvil and beneath the anvil, but danger anywhere near the system. Hail can be shot out of the top of the cell by intense updraughts
